1. Field of the Invention
The present invention relates to a surface-mount coil component having a mount surface mounted on a printed circuit board or a hybrid IC (HIC).
2. Description of the Related Art
As a coil component mounted on an inner circuit of an electronic equipment such as a personal computer or a cellular phone, there are known a winding type in which a copper wire is wound around a ferrite core, a lamination type in which a coil conductor pattern is formed on the surface of a magnetic sheet of ferrite or the like and the magnetic sheet is laminated, and a thin film type in which an insulating film and a coil conductor of a metal thin film are alternately formed by using a thin film formation technique.
Patent document 1 (JP-A-8-203737) discloses a common mode choke coil as a thin film type coil component. Patent document 2 (JP-A-2003-217932) discloses, as a thin film type coil component, a common mode choke coil array in which two common mode choke coils are arranged side by side. The common mode choke coil has such a structure that two coil conductors having almost the same shape are laminated through insulating film between two magnetic substrates arranged to be opposite to each other. FIGS. 6A and 6B show an arrangement shape of a coil conductor of a conventional common mode choke coil. FIG. 6A shows a plane shape of the coil conductor when viewed from a mount surface side of a common mode choke coil 101. In FIG. 6A, in order to make the drawing clear, only a coil conductor 133 is shown out of two laminated coil conductors 133 and 135. FIG. 6B shows a section taken along an imaginary line A—A passing through a center axis of the coil conductor 133 which is shown in FIG. 6A.
As shown in FIG. 6A, the coil conductor 133 is formed into a spiral shape on an insulating film 107b. An inner peripheral side end part of the coil conductor 133 is connected via a through hole 131 formed in the insulating film 107b to one end part of a lead wire 129 formed in a lower layer of the insulating film 107b and indicated by a broken line in the drawing. The other end part of the lead wire 129 is connected to an internal electrode terminal 121 formed at a peripheral end part of the insulating film 107b. An outer peripheral side end part of the coil conductor 133 is connected to an internal electrode terminal 125 formed at a peripheral end part of the insulating film 107b to be opposite to the internal electrode terminal 121.
As shown in FIG. 6B, an insulating film 107a, an insulating film 107b, the conductive coil conductor 133, an insulating film 107c, the conductive coil conductor 135, an insulating film 107d, an insulating film 107e and an adhesive layer 111 are laminated in this order between magnetic substrates 103 and 105. The coil conductor 135 is formed into a spiral shape almost similar to the coil conductor 133, and faces the coil conductor 133 through the insulating film 107c. Besides, the coil conductor 135 is connected to a lead wire (not shown) formed on the insulating film 107d via a through hole (not shown) formed in the insulating film 107d. 
The coil conductors 133 and 135, the lead wire 129, and the lead wire connected to the coil conductor 135 are embedded in an insulating layer 7 including the insulating films 107a, 107b, 107c, 107d and 107e to constitute one choke coil. The coil conductor 133 is connected via the lead wire 129 and the internal electrode terminals 121 and 125 to external electrodes (not shown) formed around the magnetic substrates 103 and 105 respectively. Similarly, the coil conductor 135 is connected via the lead wire and the internal electrode terminals to other external electrodes (not shown) formed around the magnetic substrates 103 and 105 respectively.
Incidentally, as electronic equipment such as a personal computer or a cellular phone is miniaturized, an electronic component such as a coil component or the like is required to miniaturize a chip size and to reduce the thickness of the component (to reduce the profile). The winding type coil has a problem that the miniaturization is difficult from the limitation in structure. On the other hand, the lamination type coil and the thin film type common mode choke coil 101 can be miniaturized and reduced in profile.
Besides, in order to raise the impedance of the common mode choke coil 101, it becomes necessary to raise the relative permeability of the magnetic substrates 103, 105 and the insulating layer 107 and to increase the number of turns of the coil conductors 133 and 135. However, in any material, as the frequency of a current supplied to the coil conductors 133 and 135 becomes high, its relative permeability is decreased, and accordingly, there is a problem that high relative permeability is hard to obtain in a high frequency band.
Besides, in order to increase the number of turns of the coil conductors 133 and 135, it is necessary to reduce the conductor width and to narrow the pitch. However, as the common mode choke coil 101 is made smaller, it becomes difficult to thin the coil conductors 133 and 135 and to narrow the pitch.
In the section including the center axis of the coil conductors 133 and 135 shown in FIG. 6B, the number of wiring lines of the coil conductors 133 and 135 is different between the right and left portions with respect to the center axes. The number of magnetic flux lines generated by applying power to the coil conductors 133 and 135 becomes large as the number of wiring lines becomes large. In a case where an interval between the outermost periphery of the coil conductors 133 and 135 and the side part of the magnetic substrates 103 and 105 is made an interval c, since the number of magnetic flux lines generated is small in the region where the number of wiring lines is small, the magnetic flux lines can pass through the region between the outermost periphery of the coil conductors 133 and 135 and the side part of the magnetic substrates 103 and 105. Thus, when power is applied to the coil conductors 133 and 135, a magnetic path M passing through the magnetic substrate 103, the insulating layer 107 of the inner peripheral part of the coil conductors 133 and 135, the adhesive layer 111 on the insulating layer 107, the magnetic substrate 105, the adhesive layer 111, and the insulating layer 107 of the outer peripheral part of the coil conductors 133 and 135 in this order is formed in the region where the number of wiring lines is small.
However, in the region where the number of wiring lines is large, since the number of magnetic flux lines generated is larger than that in the region where the number of wiring lines is small, part of the magnetic flux can not pass through the region between the outermost periphery of the coil conductors 133 and 135 and the side part of the magnetic substrates 103 and 105, and leaks to the outside of the common mode choke coil 101. Thus, the inductance of the coil conductors 133 and 135 can not be sufficiently increased, and there is a problem that it is difficult to sufficiently raise the impedance of the common mode choke coil 101.
In the common mode choke coil array disclosed in patent document 2, two common mode choke coil elements arranged to be adjacent to each other in a chip element body are arranged so that the number of turns at the side where they are adjacent to each other becomes smaller than the number of turns at the side where they are not adjacent to each other. Thus, the portion of the common mode choke coil element in which the number of turns is large is disposed at the peripheral end side of the magnetic substrate. Accordingly, when the common mode choke coil array is made smaller, the interval between the outermost peripheral part of the common mode choke coil element and the peripheral end part of the magnetic substrate becomes short, and part of the magnetic flux lines generated by the common mode choke coil element leaks to the outside of the common mode choke coil array, and there is a problem that the impedance can not be sufficiently raised.
When the interval c between the outermost periphery of the coil conductors 133 and 135 and the side part of the magnetic substrates 103 and 105 is made long in order to prevent the magnetic flux line from leaking to the outside of the common mode choke coil 101, the common mode choke coil 101 becomes large, and accordingly, there is a problem that the component can not be made smaller.